1. Field of the Invention
The present invention relates to a plasma processing system and method, and more particularly to a plasma processing system and method with inductive coupling.
2. Discussion of the Background
Conventional plasma reactors used in semiconductor manufacturing have round parallel plate electrodes. A sample typically rests on a lower electrode and a plasma is formed above the sample to create reactive species to carry out deposition or etching operations. The power is coupled to the plasma capacitively.
For large area depositions, such as polycrystalline silicon deposition to form flat panel displays, it is difficult to use the round parallel plate reactors since larger area deposition requires larger electrodes which complicates the deposition process. Also, the machine becomes larger, greatly increasing its cost and the cost to use such a machine, since clean room floor space is very expensive.
A line plasma source has been developed, as described in application Ser. No. 08/383,495, the disclosure of which is herein incorporated by reference. A diagram of the source is shown in FIG. 1. A semiconductor wafer 20 with a top surface 20S is shown being transported in a transport direction (depicted by arrow 22) relative to plasma source 24 in a plasma reactor 25. Plasma source 24 includes a plasma chamber 30. Plasma chamber 30 includes walls for defining an essentially elongated narrow rectangular volume. Plasma chamber 30 includes chamber sidewalls 34SL and 34SR, and chamber top wall 34T. A face of plasma chamber 30 opposite chamber top wall 34T is open, forming a chamber outlet aperture. A plasma 44 is generated in the upper portion of the chamber and active species exit the chamber through a long, narrow “line” outlet where they react with a reactive gas or gas mixture on the sample surface. The sample is translated past the plasma line source and the film grows on the sample in a linear fashion. The power is applied to the reactor shown in FIG. 1 with an electric field applicator 50 encased in shield 52. The electric field applicator is positioned outside of the plasma chamber to couple an electric field through the plasma. Quartz windows 48 are disposed in the plasma chamber in the vicinity of the electric field applicator.
The above system has a problem when running at high power levels. The reactor has both current and capacitive components and at high power, and the capacitive component creates difficult problems for plasma reactors. At low frequency operation, the ions may develop significant kinetic energy from the applied a.c. field which may damage the electrodes or chamber walls and which may lead to contamination of the product. Typically the reactors are operated at higher frequencies so the ions cannot react to the a.c. field thereby to avoid collisions. However, operating the reactor at higher frequencies does not solve the problem. While the ions cannot follow the field reversal, a voltage develops between the plasma and the surroundings, termed the self-bias voltage. This DC voltage can accelerate ions into the walls resulting in chamber erosion, contamination of the work product and damage to the work product.
The line source is advantageous in forming large area polycrystalline silicon films. The problems described above occurs when forming such films since the depositions times are not short, increasing the possibility that some of the ions accelerated due to the self-bias will collide with the walls and/or with the product.